Which two methods are generally used for changing capacity on demand in a heat pump?

Using a two-speed compressor in conjunction with a two-stage thermostat is an effective method for changing capacity on demand in a heat pump. This approach allows the system to operate at different capacities depending on the heating or cooling needs of the space.

When the system demands lower capacity due to milder outdoor conditions or a decrease in indoor load, the compressor can operate at a reduced speed, allowing for efficient energy use while still providing the necessary heating or cooling. Conversely, when more capacity is required, the compressor can switch to its higher speed, effectively meeting greater demand quickly.

The two-stage thermostat plays a critical role in managing this process by determining when to activate each speed level based on the indoor temperature setpoint and the current indoor conditions. This results in improved comfort levels and energy efficiency, as the system can adjust its output without having to turn off and on frequently, which can lead to wear and tear on the system.

This method contrasts with other options such as single stage motors, which offer limited capacity modulation, or manual controls that do not automatically adjust based on demand, resulting in less optimal performance and efficiency.